Yamaha Problem

[cjg]

My Yamaha V6 Oil Injected 150hp 1987 motor has the following problems..<br />I cannot get past 3500 rpm and it keeps losing power and almost stopping before going again.<br />I ran it on 50:1 premix for a short time before getting a new control unit for the oil.<br />I was just using up the fuel I had premixed.<br />Maybe it's the fuel or have they damaged the spark plugs or is it a fuel supply problem.<br />I had the idling ajusted and a compression test done when they fitted the new control unit and all was ok.<br />Any help would be appreciated.

 

[ghostrider]

Re: Yamaha Problem

cjg how much pre-mix gas did you have left in the tank? Are you getting a lot of smoke? Worst case scenario check new unit make sure it was not defective. Good luck!

 

[cjg]

Re: Yamaha Problem

I had 3 x 24 litre tanks premixed 50:1 which I was told I could still use rather than waste.<br />The control unit is brand new and it is fine.<br />There is alot of smoke but only when starting.<br />The motor starts usually first time no problem.

 

[Capt Ken]

Re: Yamaha Problem

Check your fuel pumps. You have two of them and when one goes out, it does what you are describing. One pump will only take it up to three grand or so before the carbs run dry. Heck, due to the age of the engine, rebuild both of them. Rebuild kits are cheap.

 

[cjg]

Re: Yamaha Problem

Thanks Capt Ken<br />Can you describe where I locate the fuel pumps and what to look for to check them<br />Gotta get this runnin b4 xmas

 

[Capt Ken]

Re: Yamaha Problem

Port side, just behind the carb cover but ahead of the starter. Follow the fuel lines from the carbs. They are stacked one above the other.

 

[cjg]

Re: Yamaha Problem

Found the fuel pumps.<br />How can I actually check the fuel pumps..can I open them and check anything inside..what do I look for ?<br />I have bought new spark plugs and will change all 6..anything special needed to be done ?

 

[Solittle]

Re: Yamaha Problem

Suggest you get a manual. You will need it for this and any other future maintenance/repair.

 

[Trevor]

Re: Yamaha Problem

try changing plugs first sounds like you are having problems these yamaha run any where from 50:1 down to 100:1 depending on your RPMS so I would say you have fould you r plugs also It is just a myth that more oil is better for you r motor. it can cause the needle bearings to slide rather than roll. the only time you should do this is at initial start up in the spring after winterizing you boat. Also you may have faulty T-stats if themotor is running too cold it will foul plugs causing low wide open throttle (wot)<br />Good luck.

 

[cjg]

Re: Yamaha Problem

Thanks Trevor <br />I will try the plugs and take it for a run first<br />Thanks for explaining what wot means

 

[Trevor]

Re: Yamaha Problem

let us know what happend <br />cheers

 

[cjg]

Re: Yamaha Problem

I have changed the spark plugs and it has improved slightly<br />I can now get just over 4000rpm<br />Can anyone explain how to check the fuel pumps..what do I look for<br /><br />Thanks

 

[Bear]

Re: Yamaha Problem

http://marinemechanic.com/2000/images/ob_fuelpump.htm <br />"The other critical component of the fuel pump is the two opposite facing check-valves. The use of dirty or improper fuel-oil mixtures can cause check valve problems."

 

[Hawkeye1]

Re: Yamaha Problem

You may be too late on the fuel pumps. When they go bad the diaphram splits and can contaminate the carbs high speed jets causeing you to loose lots of power. The oil injection system will provide oil so you can fowl the plugs quickly if this is the case. Pull the fuel pumps off and pull them apart. Easy to do and not much to them and at that age they need replaceing anyway. Yamaha has a upgraded fuel pump because of problems from about '92 back. One way to tell if the carbs jets are cloged is to run the boat at wot with the cowl and carb cover off and look down the throats of each carb. You will see a fan shaped fuel spray comming out the bottom of the carbs and sucking back into the engine if all is well. Compair all 6 and all should look tyhe same. If some are just dribbling fuel then you know where your problem is. All this is speaking from 10 years experience running a 1990 200 yamaha. Same baisic engine as yours. Carbs can be pulled abart and cleaned without any parts or gaskets, just be careful. Done it 3 times on 3 diferent engines in the last 20 years with no problems.

 

[rons boat]

Re: Yamaha Problem

To eliminate fuel pumps as a possiblity of causing a problem try lifting the fuel source,tank, above the engine. This uses gravity to feed the carbs just like when this all started. The tank was built in to the top of the motor.

 

[cjg]

Re: Yamaha Problem

It has been suggested that the wrong size prop could cause my Yamaha 150 to not get past 4000 rpm's<br />Can someone please tell me how to measure the prop and what should be the correct size<br /><br />I have not yet checked the fuel pumps as suggested because I am not sure what exactly to do and don't want to risk any damage

 

[rbu]

Re: Yamaha Problem

If your fuel pumps are original, it's probably a good idea to change them. Older pumps have some hardware inside them that has a tendency to rust. This small deposits can find their way into your carbs. Relatively speaking, the pumps are not that expensive, just change them, I wouldn't bother with rebuilding them.<br /><br />You should get a repair manual, there is a procedure for checking the fuel pumps, but from what I remember, you need some sort of fitting to insert into the output line and a meter to measure the pressure. It's probably easier to just replace them.<br /><br />What size boat do you have? What is your current prop size?

 

[Capt Ken]

Re: Yamaha Problem

Let me get off the floor from laughing. Just the picture of some guy trying to look in the throat of each carb while running wide open across the bay then standing up and holding a fuel tank above his head. Water cops would have him in the tank for sure believing he was drunk. Screw the prop. Unless someone has changed the prop from what it use to be, its OK. If you want to double check the fuel pumps, have someone squeeze the primer bulb while running. If he engine picks up, change the pumps.

 

[Hawkeye1]

Re: Yamaha Problem

Capt ken, I never said to hold the gas can over your head. I would just put new pumps on and try it. Then if the rpms dont come up I would go to the carbs. Looking into the carb throats is easy at wot on calm water. Only takes about a 15 sec look and you dont need a light but the light reflects off the gas and makes it stand out better. Thats the fast and easy way to determin what carb has the problem. This is a old mechanics trick. With 6 2 brl carbs that saves time. Just pull the affect carb off and pull the float bowl and find the jets and clean them out. You can even use wd-40 and back blow the dirt out in a pinch. Hold it over a clean paper towl or rag to idenitify what comes out and to make sure you get it. We have had to do this on hotel counter tops b4 on fishing trips. If the prop is the same one it use to turn up then that aint the problem. To be that much off it would have to be 6" of pitch too much but that sound like a carb down to me. These thing have 2 fuel pumps and both would have to be out to not run over 4000. Mine would turn wot for about 30 sec b4 falling off with one pump bad but would keep up and any rpm undetr 5000.

 

[rons boat]

Re: Yamaha Problem

Interesting discussion. Lot's of us have different techniques for accomplishing the same thing. The only job of the diaphram operated pump is to fill the carb bowl(s) with fuel. Lifting the tank above the bowl, priming the bulb, all accomplish the same thing and eliminate the fuel pump from consideration as a problem. Most of the time lately I have found the carbs really get crudded up fast due to the instablity of recent fuels and so have to be removed to be cleaned. I think it is interesting to see the actual flow by looking at WOT, but for some of us that is tough. I use Sea Foam and have been having some success for clearing mildly clogged carbs. It seems to help in fighting the terrible quality of gas we are getting lately. Most of the manuals I use suggested its use and I think who ever wrote them are on to something. But it will not overhaul a real dirty carb or remove a tiny piece of trash caught in the carb. A small piece of plastic will mess up performance bad and has perplexed many mechanic. My buddy with the same problem you guys are talking about would have cleaned the carbs as routine. If you don't want to do that try running a tank of gas with sea foam. What have you got to lose? Always run out the gas at the end of operation.